On 10/30/24 2:47 AM, Leon Hwang wrote:
From: Leon Hwang <leon.hwang@xxxxxxxxx>
This patch addresses the bpftool issue "Wrong callq address displayed"[0].
The issue stemmed from an incorrect program counter (PC) value used during
disassembly with LLVM or libbfd. To calculate the correct address for
relative calls, the PC argument must reflect the actual address in the
kernel.
[0] https://github.com/libbpf/bpftool/issues/109
Fixes: e1947c750ffe ("bpftool: Refactor disassembler for JIT-ed programs")
Signed-off-by: Leon Hwang <leon.hwang@xxxxxxxxx>
The following is the LLVMDisasmInstruction() description in
llvm-c/Disassembler.h:
/**
* Disassemble a single instruction using the disassembler context specified in
* the parameter DC. The bytes of the instruction are specified in the
* parameter Bytes, and contains at least BytesSize number of bytes. The
* instruction is at the address specified by the PC parameter. If a valid
* instruction can be disassembled, its string is returned indirectly in
* OutString whose size is specified in the parameter OutStringSize. This
* function returns the number of bytes in the instruction or zero if there was
* no valid instruction.
*/
size_t LLVMDisasmInstruction(LLVMDisasmContextRef DC, uint8_t *Bytes,
uint64_t BytesSize, uint64_t PC,
char *OutString, size_t OutStringSize);
In the above, it has
The instruction is at the address specified by the PC parameter.
To call insn itself only encodes the difference between
helper address and 'bpf_prog + call_insn pc within prog'.
So to calculate proper final call address, the bpf_prog entry address
must be provided. So we need to supply 'prog_entry_addr + pc' instead
of 'pc'.
32bit should be okay since addr is within the first 4G.
Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx>
---
tools/bpf/bpftool/jit_disasm.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/tools/bpf/bpftool/jit_disasm.c b/tools/bpf/bpftool/jit_disasm.c
index 7b8d9ec89ebd3..fe8fabba4b05f 100644
--- a/tools/bpf/bpftool/jit_disasm.c
+++ b/tools/bpf/bpftool/jit_disasm.c
@@ -114,8 +114,7 @@ disassemble_insn(disasm_ctx_t *ctx, unsigned char *image, ssize_t len, int pc)
char buf[256];
int count;
- count = LLVMDisasmInstruction(*ctx, image + pc, len - pc, pc,
- buf, sizeof(buf));
+ count = LLVMDisasmInstruction(*ctx, image, len, pc, buf, sizeof(buf));
if (json_output)
printf_json(buf);
else
@@ -360,7 +359,8 @@ int disasm_print_insn(unsigned char *image, ssize_t len, int opcodes,
printf("%4x:" DISASM_SPACER, pc);
}
- count = disassemble_insn(&ctx, image, len, pc);
+ count = disassemble_insn(&ctx, image + pc, len - pc,
+ func_ksym + pc);
if (json_output) {
/* Operand array, was started in fprintf_json. Before
